This invention relates to configuration and reconfiguration of storage elements in a storage system. More particularly, it relates to the configuration and reconfiguration of such elements in order to permit removal of one or more of the elements for servicing or other reasons.
There can be occasions when it is desirable or necessary to take one or more elements of a multielement storage system off line. One typical reason for doing this is the occurrence of a predetermined threshold of errors within a given element. However, if crucial (essential) portions of system programming (or system date) are within the storage element that is to be taken out of the operational system, the system will not be able to continue processing if the element is simply removed. For this reason, it was common in the prior art not to remove a storage element if it contained essential data or programs unless its removal were absolutely necessary. The removal typically would be accomplished at the end of processing, and would be followed by a new initial program load into the remaining storage elements, and substantially complete reinitialization of the storage system.
One of the reasons for the brute force approach mentioned above, was that the crucial material (data and/or program) within an element that was to be taken off line might occupy large amounts of storage and might have been assigned to the storage in any of various interleaving or other algorithmic schemes, some involving great complexity. Thus, it was not practical to simply rewrite the contents of the element that was to be taken off line into some other storage element, unless there were another storage element standing idle to be used as a spare for just such emergencies. Keeping such spares on hand is, of course, a significant added expense to a system, and is not desirable unless absolutely necessary. Another approach that could be used would be to restrict the use of certain storage elements only to temporary material which would not be needed in the event of reconfiguration of a system. However, this would introduce additional complexity into the assignment and reassignment of addresses during processing and thus could impact the throughput performance of a system. Also, a storage system in which various elements are pre-dedicated only to certain types of material will generally require more storage in order to accommodate varying workloads than a system in which all elements can be used for any type of material.